This application relates to image sensors, and more particularly, image sensors that have optically black pixels.
Image sensors are commonly used in electronic devices such as cellular telephones, cameras, and computers to capture images. In a typical arrangement, an electronic device is provided with an array of image pixels arranged in pixel rows and pixel columns. The image pixels contain a photodiode for generating charge in response to light. Circuitry is commonly coupled to each pixel column for reading out image signals from the image pixels.
Image sensors of this type may include optically black pixels arranged around the periphery of the array of image pixels that are used to generate image signals. The image sensor may be provided with light-blocking structures over the optically black pixels to help prevent light from reaching the optically black pixels and causing the optically black pixels to generate electrical charge in response to the light. In this way, optically black pixels may be used to make dark current measurements that can be used for noise compensation in image signals and for image sensor calibration operations.
Dummy pixels may be provided between the array of image pixels and the optically black pixels to allow for manufacturing tolerances. However, light that enters the image sensor through the dummy pixels may be redirected to the optically black pixels, causing the optically black pixels to generate current in response to incident light. This can produce inaccurate dark current measurements and lead to improper noise compensation and calibration.
It would therefore be desirable to provide image sensors with light-blocking structures for optically black pixels.